Hydrogen chloride recovery



HYDROGEN CHLORIDE RECOVERY Filed Dec. 21, 1955 2 Sheets-Sheet 1 FIGURE1.

March 18,

Filed Dec. 21, 1955 M. L. GOULD HYDROGEN CHLORIDE RECOVERY 2Sheefs-Sheet 2 FIGURE 2.

United States Patent 2,827,129 HYDRGGEN CHLORIDE RECOVERY 5 Merle L.Gould, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y.,a corporation of Delaware Application December 21, 1955, Serial No.554,457 4 Claims. (Cl. 183115) This application is acontinuation-in-part of Serial No. 474,826, filed December 13, 1954, nowabandoned.

This invention relates to the resolution of certain process gasmixtures. More specifically, the invention relates to the resolution ofa process mixture including substantial proportions of hydrogen chlorideand ethane, particularly such process streams obtained in an ethanechlorination.

The manufacture of lower molecular weight alkyl chlorides can beaccomplished by three general methods. In the preparation of ethylchloride, for example, ethanol can be reacted with hydrochloric acid, orhydrogen chloride can be reacted with ethylene, or ethane can be treatedwith chlorine to form ethyl chloride by substitution chlorination. Thelatter reaction otters sizeable basic economies and advantages becauseof the appreciably lower cost of alkane hydrocarbons relative toequivalent amounts of a corresponding alcohol or olefin, providing thatthe hydrogen chloride can be recovered and used, and further providedthat a high conversion of the ethane can be achieved. As is well known,in the substitution chlorination of an alkane, approximately one-half ofthe chlorine reacted appears in the products as hydrogen chloride. It isfurther well known that a chlorination process should be operated with asubstantial excess of ethane, or, stated conversely, that an appreciablecon centration of ethane is always found in the product gases.

It has been proposed to take advantage of the ultimate economies of thechlorination reaction by reusing the hydrogen chloride in ahydrochlorination process, and also recirculating the excess ethane tothe ethane chlorination operation. However, a hydrochlorination processcannot tolerate too great dilution with ethane gas, and similarly it isof course unworkable to recycle all the hydrogen chloride present to achlorination process. Hence, in order to economically carry out achlorination of ethane, it is essential to provide economical means ofresolving the product gases to efiect a resolution into an ethaneenriched gas stream, and a hydrogen chloride enriched stream as Well asrecovering the chlorinated ethane primary product. 55

Prior general methods of isolating hydrogen chloride from gaseousmixtures of this general character have included several general types.Absorption in aqueous solution is frequently employed, but non-metallic,low pressure equipment is demanded, because of the extreme corrosivityof aqueous solutions. Selective absorption of the hydrocarbon componentsof the mixture in added hydrocarbons has been utilized in other similarmixtures. Glacial acetic acid has been suggested for a hydrogen chlorideabsorbent. Liquefaction of the hydrogen chloride-alkane components andsubsequent fractionation has been proposed, but this technique would notbe beneficial for the hydrogen chloride-ethane system because thesecompounds form a constant boiling mixture. A pressing need then hasexisted for the economical resolution of the products of an ethanechlorination process.-

Accordingly, a principal object of the present invention is to provide anew and improved process for the resolution of a stream derived from anethane chlorina tion into an ethane enriched gas stream and a hydrogenchloride enriched gas stream. Another object is to provide a product gasseparation process of the character escribed which is particularlysuitable for operation at elevated pressures and which does not requireexpensive and fragile corrosion resistant equipment. Yet another objectis to provide a process which accomplishes the stated resolution into ananhydrous ethane enriched stream and an anhydrous hydrogen chlorideenriched gas stream, these streams being particularly suitable withoutfurther refinement for subsequent reusage.

The process of the invention comprises, in its most general terms, thecontacting of a gaseous mixture with a chlorinated ethanes liquid underelevated pressures and in certain proportions defined more fullyhereafter, the gaseous mixture being predominantly, on a chlorinatedethanes free basis, hydrogen chloride and ethane. A portion of the gasstream is dissolved in the liquid phase, this dissolved portion orsolute being substantially enriched in hydrogen chloride. An enrichedhydrogen chloride gas is then obtained by selective vaporization of thehydrogen chloride from the solution. In the absorption of a' hydrogenchloride enriched stream, the undissolved gas is enriched in ethanecontent. The degree of enrichment can, as will be shown hereafter, bevaried greatly to meet the needs of a particular operation. Similarly,the composition of the liquid used is variable in a wide latitude,except that it should be substantially all chloroethanes, and, further,that the average chlorine content should be less than about 1.4 atoms ofchlorine per atom of carbon, and, preferably should have an averagecomposition of from about 0.5 to 0.6 atom of chlorine per atom ofcarbon.

In general, best results are obtained using hydrocarbon chlorides having5 carbon atoms and lower. The preferred hydrocarbons contain 2 to 3carbon atoms, i. e., ethanes and propanes. The preferred chiorine atomto carbon atom ratio should be between 0.3-1. The preferredchloroethanes include ethyl chloride, ethylene dichloride, propylchloride, and propylene dichloride. Other typical examples of otherchlorinated alkanes are methyl chloride, tetrachloro propane,n-chlorobutane, dichlorobutane, and chlorohexane.

The surprising feature of the process is that, whereas other processeshave been disclosed wherein a chlorohydrocarbon is employed as anabsorption medium, in such instances the hydrocarbon component waspreferentialiy absorbed. Likewise, other solvents such as oxy compoundssuch as dioxane have been used for extracting hydrogen chloride fromboth the lower hydrocarbons and halogenated hydrocarbons. In contrast,according to the present process, the enrichment is in the reverseorder, i. e., the hydrogen chloride is enriched in the liquid phase andthe ethane is enriched in the gas phase by the initial step of theprocess. A further important aspect of the invention is the discoverythat the azeotrope mixture of hydrogen chloride and ethane is resolvedby the present method. Thus, even though the feed stream being processedcontains, as it frequently does, hydrogen chloride and ethane inproportions generally corresponding to azeotrope compositions, thedesired resolution is readily accomplished.

The benefits of the process can be obtained in a variety of embodimentsyielding varying degrees of separate eurichment. The demands of relatedoperations will determine primarily the specific embodiment to beemployed. Thus, in certain situations a sloppy separation is all that isnecessary and in such an environment a relatively simple embodiment ofthe process is preferred Thus, in situations where a subsequent ethaneestate consuming stream and a subsequent hydrogen chloride consumingstream will tolerate relatively large quantities of the other componentas an impurity (i. e., hydrogen chloride in ethaneor conversely,ethaneQin hydrogen chlorine), a simple enrichment is feasible. In.othersituations, of which fan example is a subsequent, chemicaloxidationof the hydrogen chloride toregenera t eta rela- 'tively' purechlorine streamfla rather complex emhodi- V ment of the invention isdesired'to secure-the necessary enrichment.

Although'not limiting, generally the embodiments of the process includethe following major .variationst @gingle-sta'g'e condensation-v'l'hisembodiment is the simplest mode of applicatiomof the invention. Thegembodiment involves contacting the stream to be resolved with' a "liquid'chloroethanesfljstiieam jot. the: character described, underelevatedpressure :cdndit ionsltoLres ult in formation of 'a' liquid phasewherein 1 the .chloroethanes components are not less than 15 56115601mo1e,p and 'thefs'olut'e: is. enriched in hydrogenchloride.etundissolved gas stream is enrichedeth ane overi the originalcomposition. Thegasa nd liquid phases are ,separated,

is fractionated to separate-thehyand the liquid. phase r drogen chlorideenriched solute from tliephase.

Multistage absorption and fractionation-In this emsediment,substantiallytthesame operations are earried out except that the degreeof enrichment is .enhanced hy employing almulti-plate absorption columnfor contacting the feedg'as' stream with the'chloroethanes solvent,

*Multi-stage'ahsorption with .reboiling This embodiment isfai furtherrefinement in that in .theahsorption stage laireboiling operation isconducted jointly with the multiesta'ge counter-current absorptionresulting in even greaterenrichmentand sharpness of separati-on.

'- E tractive A distillat'iongfln this' {embodiment of the g th ini ia Ib t fip ep i f th efined by fprovidinglanfove'rhead condenser for a.muiti-stage cpntacting tower in" addition "to" the reboileriforproviding lower eth ane content in th'elliq'uidfstream removed .from'this' step'. V

In'all of the foregoing species of the invention the supplementalor'secondf stepfof isolatingthe hydrogen chlo- V ride enriched streamfrom thechloroethanes liquid from 'the first stage may' he" .carried outsimilarly invarying "degrees of complexity. Generally, it is preferredto opcrate this stage 'ofjthe process as amulti-fstag'e fractionationoperation and 'at a higher temperature;than th e first gage}. 1 t.

The detailsof thecharacteristics of the materials employed in the'procesjs and in the seve'ral embodiments "thereof will bemore'readily,understood from thedetailed description given hereafter gnar om theaccompanying "figures, where f {Figure '1 is'la schematic iiow gdiagramshowing the process flows and. generalized equipment;arrangement for mpk i fi e ressss invel in ig stage a q qn nd -s i l l St g ya ri ati niopon and Figure 2 is a Similar emati flew .si rem 9f an embodiment P v di9 h hes e espf separate enrichment of thestreams;

The'examples an detailedidescriptiongiven hereafter willibe more readilyunderstood withthe aidof a prelimin/expla of the .anpar t s a ran ementshow i the above cited figures. Referring to figure}, th ill trit t ppaatu q l hemost rai t o wardem 951 inentsbr'the process of the invention,v vher ein a srngle sta c t ct n s p; is't ollqwed i y .a sing st e seond vapor n tep: vinstallation incl d es acontactor 11 and a yaporizer21. The contactor 11" is a v A complexity, including desired internalZelementS 'fQI' intii tet q f a in o 5 and iquid .st e mszqene al y,

1 in a on O -Ih d um i t lassu e an n imate-and s, ttil bril m C nta ofth componen s fed-tltereto-zans The .priu pahunits of the discharged atthe conditions of operation. 'lfhe vaporizer 21 is similarly a simpledrum or tower, fitted or provided with a heat providing shell-22,wherein a heating medium can'be introduced through heating medium feedline 23 5 and discharged through an'outlet line 24. The feed lines tothe equipment include a gas feed line 12, and a liquid feed line 13,both feeding lstreams to the contactor 11. The gas teed line 12. entersthe contactorJLpreferably at a lowermost pointtherein; and generallythefcontactor 11, is .operated so asto naintain a ,liquid'ereservoin-ofmaterial to assure intimatcjcontactvof fthe gasrited. A liquid draw ottline1 4 provides ior cgntinuqusr or inter: mittent'withd rawal ofliquidfromthe contactor an'cl'feed to the vaporizer 21. gAn oyerheadlineis provided to remove an overhead ethane-enriched stream from thecontactor 11 and discharge it to subsequent operations such as an ethanechlorination step or for various recycle .purposes. 7 r ing th egaporizerglean equilibrium condition ais=-again provided for by heatingthe liquid fed thereinz-by the ,transter line 1 4 to provide a-tgasphase enriched in'hydrog n. chloride-wh'ch' canhe discharged through anoverhead gas line 2 6 to -asubsequentconsumingoperation such as T anethylene hydrochlorination process. ;The bottomsor liquid phase from thevaporizer 21 can betdis'charged u h 29tt9 S: u i ;.1inr2 Iheproportions;and eigplicitjdesign of: the contactor ll he cqntaeting towerAnoverheadlinefiktransmits overhead gases 1 to a rr eflux, condenser 61,which 'dis- 40 qhatgges a partially condensed strearnu through a .line'62 toa disengaging;drum.,6;a. -.T he .disengagerz63 separates the ga sphase from ;the-1iquid;phase. The .gas phase discharge-linejgt ernovesthe .smseparated-gas, and a liqui'd return iine 65 receives-;the liquid.disengaged :for returnto fthe contacting tower:-31. Additionalstreamstofithe com reeting tower 31 ,-are, -pro,vided :hy areeycledah'sorberit line and arch oiled ivlapor*l ine;42fiOmJhe'J'GbOiIGI" 41. Aghott oms line fromethe Ieboileru41-fis ailiquid -ieed' -iip e othe-yaporiz'ingtower-fil. The vaporizing tower isl2 ff l h y e multi-platefiractionation 36011111111 provided 7 with .;arehoiler 8:1 -.and tan letterhead condenser 91." A

e eboiler, and {a Vreboiler discharge line 32 transmits u i-fr m thQi1er;81. .Anoverheadlvapor line 74 om the yaporizing tower :71 feeds acondenser 91 which My cts a .partialcondensation of .theihigherboilingcom- -ponents. The condensate-line 92 transmitspar-tiallycondensedmaterials from the condenser 91 to a-disengaging drum 93. t gDisengagedzliquid is returned through a line 94 .to the vapori z ing--tower 11,and an enriched hydrogen chloride line 95 receives the disengaged gas,high in hydrogen chloride content, from a disengaging. drum 93.=Reboil'edvapor separated from "bottoms by the reboiler e eiii a aifihihisti fiestas o enri hmen 2 the s act v ,s sams n ra 'smh siimem nzt rr es than is-the embodiment-ill st a ed.jsghema ca y in side:streamc'oolerSL-and an overejd; line, SZ-fintroduces" fresh teed -;81-isreturned ;to the bottom zone of the distillation tower slineB Z fromthe 'reboiler 81divides -intoa T: but of course it will also be apparentthat a substantially higher relative investment is required.

The examples given below illustrate the respective characteristics ofseveral embodiments of the process dehydrogen chloride and ethane in theproportions of approximately one mole of hydrogen chloride to two molesof ethane. The stream is fed to the contacting tower 31, concurrentlywith a return liquid stream introduced scribed with reference to thefigures, Example I being a through line 3 this Stream Fontaillingapproximately 90 description of an embodiment wherein a single stagemole percent of e hyl chlol'lde, and less than five P contacting firststep is employed, plus a single stage seccent hyd oge chlorlde- Y F ondvaporizing operation. sorbent liquid fed through line 35 is in theproportions of about 72 moles per 100 moles of feed gas. The ab- ExampleI sorbing tower 31 is operated with an overhead pressure A feed gasstream is admitted to the contactor 11 of approximately 90 poundspersquare Inch gauge and an through line 12 and contacted with a liquidfraction thereoverheadtemperature of about The bottom in at atemperature of about 120 F. and 100 pounds peramre 18 about e bottomstream y low per square inch gauge. The liquid was withdrawn coninethane content and g In hydrogen chlorlde, t tinuously and thenon-condensed gas was discharged 5 P mole cpncentratwns of theseIOITIPOIIeIItS belllg overhead through line 15. The liquid is passed tothe III the l rtttlo 0f abPut z st CV61" vaporizer 21, maintained at atemperature f 150 head gas 1s highly enriched ll] ethane, containingonly The pressure was similarly maintained at 125 pounds per abOlltOne-tenth f HCl P mole of ethane, the square inch gauge. An overhead gasfraction, comprisethane concenttatlon b81118 80 mole D The ing anenriched hydrogen chloride fraction was di 20 bottom stream is fedthrough hne 72 to the second stage charged by the vaporization throughline 26, the bottoms ffactlollatof 71, Whlch is operated t a Pressure tP- being discharged through line 5 proximately 140 pounds per squareinch gauge, with a The gas f d through line 12 contains roughly ibottoms temperature of 190 F. The overhead gas from molal proportions ofhydrogen chloride and ethane. The the Second Stage E F contfilllsalmflst 90 P chloroethanes absorbent liquid, ethyl chloride containing25 cent hydrogen chlfmdea Whlch 15 dehvered dlrectly t 3 10 percent byweight ethylene dichloride, is employed in Subsequent opel'atlon Such asan ethlflene hydrochlol'mavarying ratio, usually of from about one tofive moles tion plant. The details of the compositions of the streamsper mole of the hydrogen chloride present in the feed in this embodimentare given in the accompanying table.

Stream Compositions-Mole Percent Component Contac- Over- Frac- Frac-Feed tor head tlonator tlonator Gas 32 Bottoms from Bottoms ver- 72Contac- 82 head 95 tor-64 Methane-CH4--. 0. 9 Ethyl911-C2Hr 3. 7EthaneC:He 49. 1 Hydrogen chloride 26. 5 Methyl-vinyl chlorides- Ethylchloride 18.9 Diehloroethanes 0. 9

Quantities-100 moles teed 100 Ratio H01: 0715.0 0. 54

Split of Fractionator Bottoms:

To Contactor 72 To Recovery 21. 5

gas. The first stage contacting is performed under elevated pressure andpreferably at low or moderate temperatures adjusted so that the liquidphase formed in the absorber is relatively high in chloroethanescomponent, that is, so that the liquid phase contains above 60, andpreferably from 75 to 90 mole percent chloroethanes. In the vaporizingstep, a high temperature and pressure is employed, this resulting inelfect, in further enrichment of the ultimate gaseous product. Thereason for the further enrichment is because it has been discovered thatthe ratio of volatilities of ethane to hydrogen chloride, inchloroethanes, decreases at higher temperatures. Therefore, in a singlestage vaporization, the hydrogen chloride driven olf is not diluted tothe same extent with ethane if the vaporizing step is performed at ahigher temperature than the recovery step.

As an example of a more highly refined embodiment of the process, theExample II following illustrates the high degree of enrichment of therespective streams which is readily realizable.

Example II A gaseous stream derived from a thermal chlorination ofethane operation is available at a pressure of approximately l10-ll5pounds per square inch gauge and a temperature of about -70 F. Thestream contains When the above examples are repeated using pure ethylchloride, a dichloroethane or chloropropane, similar results areobtained.

From the foregoing examples it will be seen that the method of theprocess provides a highly effective means of effecting readily andsimply a resolution of a hydrogen chloride-ethane stream into streamsenriched in both components. The precise manner of performing theprocess is susceptible of great variation, limited only by the followingclaims.

I claim:

1. A process of separating an anhydrous gaseous stream comprisingessentially a mixture of hydrogen chloride and ethane into an ethaneenriched branch and a separate hydrogen chloride enriched branch, saidprocess including the steps of contacting said stream under elevatedpressure with a chlorohydrocarbon scrubbing liquid having not more than5 carbon atoms per molecule and less than 1.4 atoms of chlorine percarbon atom to cause the hydrogen chloride to be preferentiallydissolved by the scrubbing liquid, forming a liquid having not less thanabout 60 mole percent chlorohydrocarbon, then separating the thus formedliquid to leave an ethane-enriched gas and vaporizing a hydrogenchloride enriched gas from the separated liquid.

2. The process of claim 1 further defined in that the

1. A PROCESS OF SEPARATING AN ANHYDROUS GASEOUS STREAM COMPRISINGESSENTIALLY A MIXTURE OF HYDROGEN CHLORILDE AND ETHANE INTO AN ETHANEENRICHED BRANCH AND A SEPA-